1. Technical Field
The present invention relates to a liquid metal ion source used, for example, in a focused ion beam system or the like, and more specifically to a liquid metal ion source provided with a function for detecting flow impedance.
2. Related Art
Conventionally, devices causing ejection of ions from a metal in a molten state are known, and utilize what is called a liquid metal ion source (or LMIS). The liquid metal ion source is used, for example, as an ion source for a focused ion beam (FIB) system. A focused ion beam system focuses metal ions using an ion-optical system, and irradiates a sample with ions. A focused ion beam system can be used, for example, in scanning ion microscope (SIM) observations, and can also perform deposition or etching of a thin film of any shape without using a mask.
With a liquid metal ion source, the liquid metal is made to stick to the surface of a pointed emitter electrode, and metal ions are drawn out by causing a convergence field at the tip of this emitter electrode. An extractor electrode and a suppressor electrode are used to generate the convergence field. A D.C. value of the metal ions ejected from the emitter electrode is called the emission current.
With the liquid metal ion source, use is suspended if flow impedance exceeds a control value, and processing is preferably carried out to return to a normal operating state. A main cause of fluctuation in flow impedance is increase in impurities or dirt being attached to the tip part of the emitter electrode. For this reason, in the event that the liquid metal ion source is used over a prolonged period of time it is preferable that the flow impedance is measured every certain time.
A flow impedance Z is represented by the following equation (1) if an amount of variation in an extraction voltage Vext is xcex94Vext and an amount of variation in an emission current Ie is xcex94Ie:
Z=xcex94vext/xcex94Iexe2x80x83xe2x80x83(1)
In the related art, the extraction voltage Vext changes by only xcex94Vext with a voltage Vsup of a suppression electrode in a steady state, and flow impedance is calculated by measuring variation amount xcex94Ie of the emission current Ie at this time.
However, in the related art, flow impedance is measured by causing variation in the emission current Ie, which means that it is not possible to measure the flow impedance while the liquid metal ion source is being used, and use must be suspended.
If the emission current Ie is caused to vary while carrying out thin film deposition or etching processing etc., the deposition rate or the etching rate will vary, making it impossible to carry out high precision film thickness control.
The inventors of this application have also invented a liquid metal ion source that keeps emission current Ie constant by controlling the voltage of a suppression electrode (in a separate application), but with the liquid metal ion source of that application it is necessary to switch to a control mode so that the voltage of the suppression electrode becomes constant when flow impedance measurement is carried out. As a result, it is necessary to interrupt usage, and the length of time required to measure flow impedance is increased by the time needed to switch to suppression mode.
On order to solve the above described problems in the related art, an object of the present invention is to provide a liquid metal ion source that can enable measurement of flow impedance in a reduced time without the need to interrupt use.
(1) A liquid metal ion source of the present invention uses an extraction electrode and a suppression electrode to extract metal ions from liquid metal attached to a tip of an emitter electrode by causing a focused electric field to be generated at the tip of the emitter electrode.
There are provided storage means for storing a function of an amount of variation in emission current and an amount of variation xcex94Vsup in the voltage of the suppression electrode as a function xcex94Ie=f(xcex94Vsup), with the voltage Vext on the extraction electrode fixed, detection means for detecting an amount of variation xcex94Vsup in the voltage Vsup on the suppression electrode when the voltage Vext of the extraction electrode is made to vary by only xcex94Vext with the current of the emitter electrode fixed, and calculation means for calculating flow impedance xcex94Vext/xcex94Ie using the voltage variation amounts xcex94Vext and xcex94Vsup acquired by the detection means and the function acquired from the storage means.
With a liquid metal ion source constructed in this manner, since it is possible to detect flow impedance without causing variation in a current value Ie of the emitter electrode, it is possible to perform this detection operation in parallel with normal operations (microscopic observation, thin film deposition or etching).
(2) A flow impedance measuring method for a liquid metal ion source of the present invention is a method of measuring the flow impedance of a liquid metal ion source, using an extraction electrode and a suppression electrode, for extracting metal ions from liquid metal attached to the tip of an emitter electrode, by causing a focused electric field at the tip of the emitter electrode.
There is provided a storage process for inputting and storing a function of an amount of variation in emission current and an amount of variation xcex94Vsup in the voltage of the suppression electrode as a function xcex94Ie=f(xcex94Vsup), with the voltage Vext on the extraction electrode fixed, a detection process for detecting an amount of variation xcex94Vsup in the voltage Vsup on the suppression electrode when the voltage Vext of the extraction electrode is made to vary by only xcex94Vext with the current of the emitter electrode fixed, and a calculation process for calculating flow impedance xcex94Vext/xcex94Ie using the voltage variation amounts xcex94Vext and xcex94Vsup acquired from detection means and the function acquired from storage means.
With such a flow impedance measuring method, since it is possible to detect flow impedance without causing variation in the current value Ie of the emitter electrode, it is possible to perform this detection operation in parallel with normal operations (microscopic observation, thin film deposition or etching).